Pulsed oscillator



May 30, 1950 A. e. KANDOIAN 2,509,235

PULSED OSCILLATOR Filed May 13, 1948 2 Shets-Sheet 1 A A A A A A A A A A-vvvv ECHO BOX P /Z6 20 a 21 J v A 14 pa; S/NG MODULHTO? T 16 IN VENTOR.

A TTOlP/VE'Y y 1950 A. G. KANDOIAN 2 509335 PULSED OSCILLATOR Filed May13, 1948 2 Sheets-Sheet 2 PULS/NG M0 DUZ 14701? PUL SV/VG MODl/L 470AINVENTOR. HEM/6 a A fl/VDO/4N Patented May 30, 1950 PULSED OSCILLATORApplication May 13, 1948, Serial No. 26,798

10 Claims.

This invention relates to radiating systems and more particularly itrelates to systems for radiating pulses of high frequency energy.

In oscillation generators of the type which are keyed by pulses intooscillation, the inherent noise effects generally may control the timeat which the oscillation becomes effective. Under these circumstancesthe timing of the pulses may not be precise but will vary back and forthin a random manner dependent upon the noise disturbance levels. To avoidthis difficulty it has been proposed to provide an auxiliary oscillator,for example of the spark gap type feeding into the oscillator moreprecisel to control the timing of pulse oscillation initiation.

It is an object of the invention to provide a source of such auxiliaryoscillations generated directly by operation of the main oscillator andnot dependent upon an external generator.

A feature of the invention relates to a selfexcited high frequencyoscillator having a generation conditioning arrangement employing a highQ resonant circuit coupled reactively to the selfexcitation portion ofthe oscillator, to render the initiation of oscillation pulsesindependent of the random noise voltage conditions within theoscillator.

Another feature relates to a self-excited oscillator of thegrid-controlled electron tube type having coupled to its self-excitationcircuits a high Q resonant cavity for the purpose of rendering the timedinitiation of the oscillation pulses independent of the random noisevoltage conditions within the oscillator.

A further feature relates to a modulated or pulsed oscillator which iscoupled reactively to an echo box for the purpose of rendering the timedinitiation of the oscillator pulses independent of the random noisevoltage conditions Within the oscillator.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood, by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

Figs. 1 and 2 are respective graph diagrams explanatory of theinvention.

Fig. 3 is a schematic wiring diagram of an oscillator system embodyingthe invention.

Figs. 4 and 5 are respective modifications of the system of Fig. 3.

In one well-known system for producing pulsed groups of ultra-highfrequency waves, a Self- 2 excited oscillator of the grid-controlledelectron tube type, has its anode voltage keyed off and on or modulatedunder control of a pulse modulator. It has been found that when thesepulsed anode voltages are applied for an extremely short interval, forexample a few microseconds at a time, the pulsed output from theoscillator is not always the same for successive equal modulatingpulses. One of the reasons for this is that the preconditioning of theoscillator as a generator,

is a function of the random noise voltage conditions existing inherentlyWithin the oscillator system. Thus, as shown in Fig. 1, the graph Irepresents the random noise voltage conditions, while the graph 2represents the output of ultrahigh frequency oscillations occurring intimespaced pulses P. It can be shown that in a self-excited oscillator,the generated oscillation waves build up exponentially from a very smallvalue to their respective peak values. It is clear therefore, that theamplitude of the inherent random noise voltage in the oscillator willhave an appreciable effect on the rate of the said exponential build-up.That is to say, if the random fluctuation should be practically nil, thebuild-up is initiated at substantially zero value on the exponentialcurve. If the fluctuation voltage is.

of some more appreciable amplitude, the build-up is initiated at a pointfurther along the exponential curve and the resulting pulse envelope forthe same energizing potential will be larger, and the wave front thereofwill occur in time relation in advance of the wave front of a pulseenvelope initiated further down the exponential curve.

In accordance with this invention, the preconditioning of the oscillatoris rendered independent of its inherent random noise voltage conditions,by using part of the wave energy from one generated pulse ofoscillations from the oscillator to maintain a preconditioning voltagewithin the oscillator of regular amplitude and frequency so as to bridgethe time interval between the successive pulses P. This preconditioningvoltage can be made of any desired level, so that when the anode of theoscillator receives its modulating pulsing potential, it always respondsat an accurately predictable instant. I have found that this result isbest achieved by using a wave energ storing device such as a high Qresonant cavity, for example the well-known "echo box that is used inradar system setups. Such an "echo box, as is well-known, comprises ahigh Q resonant cavity provided with suitable coupling loops. One ofthese loops is excited by E ultra-high frequency source, and while theenergy is being thus picked up, the echo box stores it until the end ofthe excitation pulse. At the completion of the pulse, the echo box reradiates the previously stored energy. The time elapsing between thetermination of the excita tion pulse and the dropping of the reradiatedecho to a--certain m-inimi1m, is known as the ringing time. This storagecharacteristic of an "echo box is taken advantage of in the presentinvention, by coupling the reradiated echo voltage into the ultra-highfrequency oscillator soaas to: bridge the time gaps between successiveoff and on keyings of the anode-voltage of; the

oscillator-generator. This bridging" condition is shown in Fig. 2,wherein the curves l and represent respectively the randominoiseivoltage and the generated ultra-high frequency voltage as in Fig. 1, andthe curve 3 representsth'e interpolated echo voltage above-mentioned.

4 age which can be of a single frequency and regular amplitude. If theultra-high frequency oscillator is being used as a pulse-time modulatedtransmitter, there is obtained an improved ratio of signal-to-noise.Furthermore, since the box ll is a source of highly stable frequency, itprovides a constantly acting stabilizing influence on the lessista'blefl but moretpowerful zpulsed selfexc'itd oscillator. Improvedefiiciency of the transmitter is thus obtained because the initia- 'tionof each transmitted pulse is effected more rapidlypand less of the pulseenergy is expended V in useless D. C. dissipation.

high frequency oscillator; comprising, forex-'- ample; two gridcontrolled electron tubes 4, 5; havingtheir grid me plate ircuitsintercoup'led" to generate sustained oscillat by 'weli kncwnreedbackaction; -Preferably;although-notneces eratiorr;

ris connected? tli'rcugri a tunable resonant network Ill; to"the g'rid'll'. Ina-similar manner;

Merely for'i'llustrationg-the"-netwoiks' 'i, l8 and" li4j' are ishown inthe 'draw'ing" as of the wave transmission" line" type," and tuned to"the frequency of the generated oscillations:

modulator Is -or anyweu= kncwm1indj for producing high frequenc vo1tageD. Cppulses ofaccurately"timedarid-Wlall defined wave front, isconnected b'yfas'uitable' line l6" to the electricalxfiidpoihtlof'thetuned line Hand thence'to the" arid l4, tunable" echobox" H; such as is" Well-known in raidar"systeins"; and comprising a I9,anda smalldipolefl ni having a'coupling loop 21"Wlthin theca'v'ity.Consequently, when the oscillator is' keyed on by the modulator "l5;thecavity l8 isexcit'ed by theultra-high frequency energy pick-up by.dipolezlli' Because'oif thehigh 'Q'pr lowdissipa'tionfactor of thebox[Lit continues to oscillate orr'ingfor aconsider-- able period after theexcitation pulse picked'up by"dipol e '29 has ceased. "However, b'ywe llknown theory, the wave 'energ'y stored-inbox' I is 'the'n 'reradiated{by dipole 2'8 into the ultralii'gli frequency oscillator} for example byactin onpn'e'or more of 'the lihesl'j In and l4, to set up--ple'c0nditiohin'g'- voltages within the cs cillator sy'stern asrepresented by the urves of Figl 2.

As a-specific example, let-'- it' be 'assiurr'i'ed that" thedu-ration feach pulseP (Figs. 1' and 2)' is two microsecon s, an'cl 'th'a't' the"interp'illse' interval is' t'en microseconds; and that 'the'cavity l 8ing periodof the echo b'ox can-"bemade to be asmuch-as' twentyrn'icrosecondsi- A's'a' result,' theultra high frequencyoscillator-neednotre'ly for starting or'buil'd upo'fits waves, on the in'st'an'--taneous wameef "its" inherent random noise voltage w en it--iskeyed onby-modulator l5, be cause the echo b'ox ringing-voltage will provide theos'cillator with" a=larger preconditioning voltrelay" for alternativelyapplying the" modulating mg. ershowsm modification of Fig. 3. The

iparts of-Figs.3 and 4' which are functionally identical, are designatedalike. However, in this embodiment;thee-plates l2 and 13 are connectedto thepulsing modulator [5, by means of a tunable'resonant cavity 22 bymeans of small inductive loops '23, 24, D. 0. connected to the cavity.Also coupled to 1 the cavity-space by r a"-' small =induct-ive loop 2535a small dipole 2li-i wlfrich is dl rectly or radiatively coupled to theecho box I'll- The systernof "Fig. 4; operates substantially from themodulator I5 effectivewinirormly on tlie' oscillator;

Fig.5 shows a 'I'll0dlfifiatiO1'I Of FigS; 3"-'a'nd 4E 1 It may bercu'nd that under certain'coriditions'; it"i is not practio'ablato-provide an" echobox ll havinga sumciently high Q' to provide theneees'saw-bridging ringing voltage"between 'successive I pulses from theoscillator. An' arra'nge'rnent 'for avoiding this difiiculty i's'shown'inFig. 5', wherein the ec'ho box I? is excited bye-small lo'calfultra-high frequencyoscillator?! j of' approxis" matelythe samefrequency as the ma'in' oscillator;

" The" oscillator "21' isconnectedto the'piil'sing modulator l5, soas'to-be"pulsed slightly-in"ad van'ce of'the pulsing of' the'mainoscillator, for example a few microseconds in advance tlie'reofi Theultra-high frequency energy from oscillator" 21" excites "the cavity I 8so thata'fte'r'the termina tion'of" each" pulse from'oscillatbr-'2T,"the box If rings and reradiates the ultra-highfrequency" e'nergyfro'm its dipole2hto the dipolefidass'ociate'd" withthe resonant cavity 22. 'The block"28' in Fig.5 represents any'well'knownarrangement for timing the application of the modulating pulsesltooscillator'zl slightlyin'advance o'f 'the' applicationpf thesamemodulatingfpulse' to'the main oscillator. It may'takejforexample; theform of' an electronic commutatoror electronic pulses from modulator 15to the" auxiliaryioscil' lator'" 2 Tiand to the'main' oscillator" in theproper timed relation.

While Ihave described above the principlesof" the "generation of itsoscillations" substantially aaoaaaa independent of random noise voltagesinherent in the oscillator system.

2. The method of controlling the impulsing of an electron tubeoscillator, which comprises applying instantaneous potential pulses tothe anode of the oscillator to produce spaced groups of outputoscillations corresponding in duration to the period between successivepulses, applying said output oscillations to excite and store up energyin a resonator which is capable of producing echo wave energy, andcoupling said echo wave energy to said oscillator to precondition theoscillator between successive groups of output oscillations.

3. The method of rendering an anode-pulsed self-excited high frequencyelectron tube oscillator substantially independent of its inherentrandom noise voltage conditions, which comprises setting up a highfrequency echo wave under control of the output of the oscillator, andcoupling said echo wave into the oscillator to bridge the intervalsbetween successive pulsed output waves of the oscillator.

4. The method according to claim 3 in which the echo wave is of the samefrequency as the generated oscillations.

5. An oscillator system comprising an electron tube oscillator, means toapply potential pulses to the anode of said oscillator to produce spacedgroups of output oscillations corresponding to said pulses, a waveenergy resonator device excited by the waves from the output of saidoscillator, a second resonator device producing corresponding echo waveenergy, and means for coupling said echo wave energy into saidoscillator to render the generation of its oscillations substantiallyindependent of random noise voltages inherent in the oscillator system.

6. A system according to claim 5 in which said second resonatorcomprises a high Q wave resonant cavity.

7. A system according to claim 5 in which said second resonatorcomprises a tunable resonant cavity which is radiatively coupled to theexcitation circuits of said oscillator.

8. A system according to claim 5 in which said second resonatorcomprises a cavity resonator in the form of an echo box having aradiating element coupled to the cavity and to the excitation circuitsof said oscillator.

9. A system according to claim 5 in which said second resonatorcomprises an echo box in the form of a cavity resonator having aradiation element coupled to the cavity, said radiation element beingradiatively coupled to another radiation pick-up element which in turnis coupled to a cavity resonator connected in the excitation circuits ofsaid oscillator.

10. An oscillator system comprising a selfexcited oscillator, a pulsingmodulator for applying D. C. pulses to the anode of said oscillator tokey it on and 011" an echo box coupled to the oscillator output to feedinto the oscillator between successive pulses echo waves of fixedfrequency and amplitude derived from the said oscillator output.

ARMIG G. KANDOIAN.

REFERENCES CITED UNITED STATES PATENTS Name Date Varian Jan. 8, 1946Number

